Synthesis of amorphous cobalt hydroxide nanosheets and electrochemical performance according to phase transition into crystalline cobalt oxides

Ultrathin two-dimensional nanosheets have attracted attention as nanostructures that maximize the electrochemical performance in energy storage and conversion because of their unique advantages of large specific surface areas and large exposure to active sites. Herein, we synthesized cobalt hydroxide nanosheets with an amorphous phase and a thickness of <1.5 nm. Amorphous cobalt hydroxide nanosheets grown according to the surfactant concentration were converted into crystalline cobalt oxides through a simple heat treatment. The change in the electrochemical oxygen evolution reaction performance according to this process was investigated in detail by ex- and in-situ Raman spectroscopy, and the supercapacitor performance was confirmed. This study provides promising guidelines for developing phase-dependent catalysts from cobalt hydroxide and cobalt oxides and highlights the critical role of the crystal structure in facilitating electrocatalytic processes.